target/arm: Don't decode insns in the XScale/iWMMXt space as cp insns

In commit cd8be50 we converted the A32 coprocessor
insns to decodetree. This accidentally broke XScale/iWMMXt insns,
because it moved the handling of "cp insns which are handled
by looking up the cp register in the hashtable" from after the
call to the legacy disas_xscale_insn() decode to before it,
with the result that all XScale/iWMMXt insns now UNDEF.

Update valid_cp() so that it knows that on XScale cp 0 and 1
are not standard coprocessor instructions; this will cause
the decodetree trans_ functions to ignore them, so that
execution will correctly get through to the legacy decode again.

Cc: qemu-stable@nongnu.org
Reported-by: Guenter Roeck <linux@roeck-us.net>
Signed-off-by: Peter Maydell <peter.maydell@linaro.org>
Reviewed-by: Richard Henderson <richard.henderson@linaro.org>
Tested-by: Guenter Roeck <linux@roeck-us.net>
Message-id: 20210108195157.32067-1-peter.maydell@linaro.org

target/arm/translate.c

@@ -5282,7 +5282,14 @@ static bool valid_cp(DisasContext *s, int cp)
      * only cp14 and cp15 are valid, and other values aren't considered
      * to be in the coprocessor-instruction space at all. v8M still
      * permits coprocessors 0..7.
+     * For XScale, we must not decode the XScale cp0, cp1 space as
+     * a standard coprocessor insn, because we want to fall through to
+     * the legacy disas_xscale_insn() decoder after decodetree is done.
      */
+    if (arm_dc_feature(s, ARM_FEATURE_XSCALE) && (cp == 0 || cp == 1)) {
+        return false;
+    }
+
     if (arm_dc_feature(s, ARM_FEATURE_V8) &&
         !arm_dc_feature(s, ARM_FEATURE_M)) {
         return cp >= 14;